Yes. In chapter 16 several 'ordinary signatures' (aka recipient signatures) are added to a document. While I was writing the book, 'certifying signatures' weren't supported in iText yet, but I managed to insert a small pointer on how to do it (there's very little difference from the point of view of the developer). We are expecting better support for certifying signatures in one of the upcoming releases. In the appendix, there's also an example on how to sign a PDF with a smart card (I used my Belgian eID for this), but signing with a smart card is not discussed in detail as you need middleware that can be different for each type of smartcard(reader).